The past, present, and future of bionic eyes

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Next-generation bionic eyes are practically here today. Imagine a blind person’s real-world conundrum trying to shop for one — they could schedule surgery for Nano Retina’s implant today and see their daughter’s wedding in 576-pixel clarity, but it would cost them their life’s savings. The Nano Retina 5000-pixel device could be ready tomorrow, or in another six months… and would be much more affordable. When the procedure involves assimilation of an electrode pincushion into the ganglionic tentacles of your retina, hardware upgrades are not as simple as popping in more RAM. What kind of decision matrix could be offered under such critical circumstances?

Cochlear implants, used to restore hearing, work phenomenally well when properly tuned and fitted. Most are refinements of the basic piece of hardware one might have sitting on their bookshelf — the graphic equalizer. The implant processes a single audio stream into bins of various sizes according to frequency, and then applies current to the corresponding frequency location in the cochlea, typically with a 16-spot linear electrode. The main function of these devices is to capture speech formants — the peaks in the frequency spectrum of the voice. The toughest challenge for the cochlear implant is to provide sound localization and source separation in noisy environments like a cocktail party.

Vision implants are much more complex. As any practiced photographer knows, the eye is more than a camera. The optic nerve does not feed the brain pixels. If you imagine your camera responding to auto-selected targets several times a second, gathering the full spectrum of light through its entire range of settings at each pause, and compressing the data onto a bandwidth- and energy-limited channel ideally matched to its receiver, you have some idea of what the retina accomplishes routinely.

The reason cochlear implants work so well is that the brain is just that good at making sense out of virtually any kind of signal it is given. If presented only with noise, or with nothing at all, the brain will eventually begin to manufacture hallucinations. If the implant signal contains even some distorted fragment of the original signal, it can be made to work convincingly. This is also the reason why retina implants can work without incorporating any knowledge of what the retina actually does in the healthy state.

These days researchers are trying to do a little better than the grainy images provided through our current implants. Signal processing techniques were developed in the Cold War era to track and target incoming missiles by extracting signals from noisy radar data. These same techniques are now used to convert the activity of groups of neurons in the motor cortex into a set of commands for moving a cursor, prosthetic device, or de-enervated limb in brain machine interfaces (BCIs). These methods and derivations of them can also be applied to incoming sensory data and can approximate what the retina actually does, without doing it in the same way.

Unfortunately, videos and TED talks are not the places where this kind of knowledge is typically transmitted in much depth. For that, one needs to look back to the work of the founding father of cybernetics, Norbert Wiener, and his eminently practical inspiration, Vito Volterra. After suggesting that helium be used instead of hydrogen in airships, to great success, Volterra shifted gears and came up with some methods to characterize complex systems. Wiener simplified Volterra’s equations and they are now widely used today in statistical techniques like linear regression analysis, and analysis of spike trains from neurons.

Tagged In

Great article! I’m intrigued by the statement that the brain is really good at making sense out of any signal. I wonder if I took a camera and wired it up to something that stimulated a large enough patch of skin, that after a long enough time I might start correlating what I’m seeing with my eyes with what I’m feeling in my back. Perhaps the brain might eventually start ‘seeing’ the skin stimuli as optical data.

jhewitt123

That would be a neat experiment. This report, a few hours ago, http://www.newscientist.com/article/dn22597-human-eye-proteins-detect-red-beyond-red.html raises the same kind of question. If you could suddenly get input from wavelengths longer than regular old red, well at first it might just be reddish, but perhaps you might giggle or tingle a little bit when you see with it, – it might seem richer, more saturated, even flourescent, but over time either your old color scheme would remap to fit it in and it would become the new red, squeezing the others down, or you would have a new percept altogether. I wouldn’t know exactly.

Joel Detrow

To expand our range of color, I think we’d simply have to sort out how the brain receives information for each of the three different kinds of color (some cones receive red, others green, others blue) and then use that information to add sensory inputs for higher or lower wavelengths with the same method that the brain already encodes RGB wavelengths. (i.e., add a fourth “cone” for infrared)

It may require extra neurons and pathways, but I’m sure by the time we get the mechanisms figured out, we’ll have the biological knowledge and capability to make those changes, if we even need to.

…man, I feel so lucky to live in this day and age.

VirtualMark

I think our brains can actually process UV – i was reading about some people who had a retina defect and could detect UV already! So it might be possible with the right technology!

jhewitt123

Reindeer retinas apparently detect UV well. Brain detects electrical signals on axons, well, probably acoustic pressure pulses too, maybe some stray photons propagate reliably too in myelin or microtubules. While violet is a wavelength beyond blue, purple is just blue mixed with red. To be simultaneously given detectors for UV and IR the brain might at first bin them together in a single percept as on a color wheel. As they eventually came to be understood by association to be different things, they would likely be treated as such, perhaps morphing into the shapes of the synesthetic. Color perception shifts according to its intensity and intense UV would not be desireable. If one of these new inputs popped up as a green or yellow that might be surprise but who knows?

Joel Detrow

The brain doesn’t really process UV, it processes the electrical inputs from the cells on the retina. Each type of cone cell has sensitivity to a certain range of frequencies, matching a bell curve. The frequency curve of each cone overlaps with the one next to it, and that’s probably the only reason we can see the entire range of frequencies of visible light, without gaps. Hence, for a smooth progression of color from high to lower frequencies, we would have to add a new sensory cone, overlapping with either the highest or lowest frequency range, and “wired” the same way as other cones, yet different from them in the same way that cones already differ from each other.

To help figure out what that difference is, we can probably compare the visual circuitry and cortices of dogs and humans. Dogs only have two varieties of cones, one for blue, and one for lower frequencies of visible light. (that’s why if you toss a red ball into the grass, they can’t find it – it’s all the same color unless it’s blue)

Jerry

This year I’ve become conditioned to believing there are few limits to neuroplasticity!

Joel Detrow

I’ve thought for a while that a kinect sensor could be wired to an array on one’s chest, and paired with a specialized device, the entire chest would in a sense become a blind person’s new retina.

VirtualMark

This is an awesome idea – i’d love to see that experiment done.

Nehal Ezz El Dein

Hello, I would like to know further information regarding the bionic eye for my sister.. She is unable to see with her right eye, and I was wondering who I could contact about this ..? Anyone?

jeanblake80

This is SO interesting to me. I’ve been thinking about going back to school. I would love to study to become an optometrist in Edmonton. The human body is just fascinating.

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